-- Nashville Metropolitan Transit Authority to Receive Orbital's OrbCAD XP System To Enable Comprehensive Management of Fixed-Route and

                     Paratransit Vehicle Fleets --

DULLES, Va.May 8, 2007--Orbital Sciences Corporation (NYSE:ORB) announced today that its Transportation Management Systems (TMS) division has been awarded a $7.3 million letter contract by the Nashville Metropolitan Transit Authority (Nashville MTA), Nashville, Tennessee. Upon contract finalization, Nashville MTA will receive Orbital's latest Computer Aided Dispatch (CAD) and Automatic Vehicle Location (AVL) system, known as OrbCAD XP, along with new features to help the transit authority improve the effectiveness of its fixed-route bus service and its AccessRide paratransit service. Orbital will supply Nashville MTA with a suite of real-time and analytical tools that will assist in overall operations management of its 199-vehicle fleet of buses, as well as its 25 supervisory and support vehicles.

"The new tools of Orbital's CAD/AVL system will help make MTA's services more accessible to customers," said Paul J. Ballard, Chief Executive Officer of Nashville MTA. "All passengers will benefit from this new system. For example, operators of the AccessRide paratransit service will receive turn-by-turn directions for improved reliability of pick-up and drop-off services."

Orbital will deliver the entire system in a phased approach over a 24-month period, based on a timeline requested by Nashville MTA. The company will begin with the installation of the fixed-end and onboard equipment. Later, Nashville MTA's entire fleet of fixed-route vehicles will be equipped with automatic passenger counters for more efficient service planning. Additionally, MTA's fare collection system will be integrated with the OrbCAD system to improve automation and simplify operations.

Orbital will also supply its OrbStar Mobile Data Terminal (MDT) in Nashville's AccessRide paratransit vehicles. The OrbStar color-display MDTs will provide detailed turn-by-turn navigational directions, along with updated, real-time manifests to AccessRide drivers throughout the service day as adjustments are made to passenger pick-up and drop-off times. This will benefit AccessRide's passengers because Nashville MTA will be able to more effectively respond to route and customer changes.

Mr. A. David Kachemov, Senior Vice President and General Manager of Orbital TMS, said, "Orbital is looking forward to working with Nashville MTA to install our integrated fleet management tools, which will help them continue to improve the level of its services that it offers the people of Nashville. Our flexible scheduling, innovative products and dedicated team of professionals will enable Orbital to deliver a system that benefits the Nashville MTA team by improving their situational awareness, as well as providing new customer-friendly features for fixed-route and paratransit system passengers."

Mr. Kachemov completed his remarks, adding, "This agreement clearly proves that even mid-sized transit systems, such as Nashville MTA, can realize the benefits of the OrbCAD system. Plus, the OrbCAD XP system's open architecture will allow the Nashville MTA to add new features in the future as the Music City continues to grow and demand for public transit services increases."

About Orbital TMS

Orbital TMS is a leading integrator of products for fleet and workforce management, mobile data communications, data management, and advanced traveler information systems. TMS provides integrated Computer Aided Dispatch and Automatic Vehicle Location solutions for 60 public transit and state agency customers in the U.S. and internationally, with units installed or scheduled to be installed on approximately 28,000 vehicles. More information about Orbital TMS can be found at http://www.orbitaltms.com.

About Orbital

Orbital develops and manufactures small space and rocket systems for commercial, military and civil government customers. The company's primary products are satellites and launch vehicles, including low-orbit, geosynchronous-orbit and planetary spacecraft for communications, remote sensing, scientific and defense missions; ground- and air-launched rockets that deliver satellites into orbit; and missile defense systems that are used as interceptor and target vehicles. Orbital also offers space-related technical services to government agencies and develops and builds satellite-based transportation management systems for public transit agencies and private vehicle fleet operators. More information about Orbital can be found at http://www.orbital.com.

    CONTACT: Orbital Sciences Corporation
             Barron Beneski, 703-406-5528
             Public and Investor Relations

    SOURCE: Orbital Sciences Corporation